Founder is a common cause of lameness in horses. It involves damage to the laminar connection between the hoof wall and the coffin bone.

This often leads to rotation and/or sinking of the coffin bone which causes severe pain and can permanently damage the hoof structure.

Multiple factors can contribute to the development of founder. Horses with the condition may show a range of signs of distress and discomfort and typically cannot move about comfortably.

Clinical and radiographical examinations of the hooves by a veterinarian are needed to confirm a diagnosis of founder. [1]

Prevention and treatment requires addressing the underlying causes of the condition. Founder is not always treatable if the internal structures of the foot have sustained significant damage.

Horses on lush pasture or high-grain diets are most susceptible to laminitis and founder. Metabolic issues such as Cushing’s/PPID and Equine Metabolic Syndrome (EMS) can also increase the risk.

Proper feeding, hoof care, and health management are critical for supporting hoof health in horses. If your horse is recovering from or at risk of founder, our nutritionists can help you develop a balanced feeding plan for free that supports hoof health.

What is Founder?

A debilitating and painful condition, founder occurs in the equine foot and is a common cause of lameness.

The condition affects the laminae (the soft tissues of the foot) and the coffin (pedal) bone, which plays a key role in hoof form and function. The coffin bone is situated in the front portion of the hoof capsule. [1]

The terms “laminitis” and “founder” are often used interchangeably. However, distinctions can be made between the acute phase of laminitis versus ongoing chronic issues.

Acute laminitis or a “bout of laminitis” typically refers to the sudden onset of pain and inflammation of the laminae. The term founder can be used to refer to the ongoing condition that involves rotation/sinking of the coffin bone. [2]

Not all horses with laminitis will experience coffin bone rotation (founder). However, many horses with founder will have previously had one or more attacks of laminitis.

Laminae

Each equine hoof contains approximately 600 interlocking laminae that provide structural support to the hoof. Damage to the laminae can result in:

  • Separation of the sole from the hoof wall observed at the white line of the hoof; the area between the wall and sole of the hoof
  • A long toe
  • Flat hoof sole
  • Divergent hoof rings
  • Laminitis
  • Founder

When founder occurs, there is low blood flow and and poor supply of nutrients to the laminae, which results in swelling and inflammation. An attack of laminitis and the resulting founder it can cause can lead to the death of cells in the laminae.

In a hoof affected by founder, the laminae become so damaged that they are unable to sufficiently support the coffin bone. Founder results in a change of position of the coffin bone under the influence of the weight of the horse and due to the upward pull of the flexor tendon which attaches to the base of the bone. [1]

In advanced cases of founder, the coffin bone can protrude through the sole of the hoof and cause irreversible lameness. [1] Once a horse has suffered a single founder attack, it is likely the condition will occur again.

Once founder has initiated extreme damage and pain in an affected horse, euthanasia may be the most humane option.

Prevalence and Prognosis

Half of all US horse operations surveyed in 1998 reported having at least one horse with lameness and 13% reported having a horse with laminitis.

The survey also found that 4.7% of horses with laminitis died or had to be euthanized due to the condition. [3]

In this owner-reported survey, over 50% of reported laminitis cases were thought to be due to grazing on lush pasture and grain overload.

Up to 74% of horses with laminitis recovered and were able to be used for their intended purposes.

Types of Founder

The following classifications of founder can affect horses: [4]

  • Acute founder: Occurs when the attachment between the hoof wall, the laminae, and the coffin bone suddenly sinks downwards
  • Chronic founder: Refers to acute laminitis that lasts longer than 72 hours in horses that have already had their coffin bone(s) rotate or sink
  • Support-limb founder: Affects a healthy foot that is providing weight-bearing support when there is an injury on another limb
  • Mechanical founder: Develops gradually as separation takes place between the hoof wall and the coffin bone due to a breakdown of the laminae. Overgrown hooves and chronic tension on the deep digital flexor tendon (DDFT) can initiate mechanical founder

Effects of Founder on the Foot

When rotation of the angle of the coffin bone occurs relative to the short pastern bone located above it, intense pressure is exerted on the sole of the foot potentially causing it to penetrate the sole.

A depression may be present at the front of the coronet where the joint space between the coffin and pastern bone becomes wider than normal. [4]

When the coffin bone sinks onto the sole of the foot, separation has occurred in the white line of the hoof. Separation of the white line causes the toe to appear straight although a curvature in the angle of the toe just below the hairline of the coronet band is present. [4]

In founder cases involving a sunken coffin bone, the laminar connection is no longer present which makes the rehabilitation of the affected hooves more difficult than when only rotation has occurred.

Common Causes of Founder

Founder is a complex condition that can be precipitated by both metabolic and environmental factors acting on their own or in combination with each other. [4]

Some of the most common causes of founder include the following.

Dietary Factors

Overconsumption of grain products or grass from lush or stressed pastures are the most common dietary factors that can cause laminitis and founder.

Grains and lush grasses are high in non-structural carbohydrates (NSC) including sugar, starch, and fructans. High intake of starch and sugar can overwhelm the small intestine and lead to excess carbohydrates reaching the hindgut, often called “starch overload”.

This leads to higher levels of lactic acid production in the cecum and colon, known as hindgut acidosis.

An excessive amount of lactic acid in the hindgut can disrupt the microbial population and cause the death of these hindgut microbes. As acid accumulates in the intestine, it also causes damage to the gastrointestinal lining.

Absorption of Dietary Toxins

Horses with a compromised gastrointestinal lining absorb more toxins into their bloodstream. A common source of toxins is bacterial endotoxins which exist in the cell wall of bacteria.

Upon entering the bloodstream, these toxins lead to activation of matrix metalloproteinases (MMPs) that damage the hoof laminae, thus increasing the risk of laminitis and founder.

Research investigating metabolism-related causes of laminar damage suggests that a sugar metabolite called methylglyoxal (MG) may be responsible for damage in the feet of horses.

MG produced during the digestive process in horses could be absorbed into the bloodstream and alter the structure of the hoof laminae. [5]

Metabolic Disorders

Hormonal imbalances including Equine Metabolic Syndrome (EMS) and Cushing’s Disease (Pituitary Pars Intermedia Dysfunction) are associated with an increased risk of laminitis.

In a study of horses that presented at a Finnish veterinary hospital due to laminitis, 89% had evidence of underlying endocrine disorders. One-third were diagnosed with PPID and the remainder had high insulin levels indicative of insulin resistance but without signs of PPID. [6]

Insulin resistance is particularly high among overweight/obese horses, of which 95% have high levels of insulin but without signs of PPID. [6] Overweight/obese horses are at higher risk of developing laminitis and founder due to chronically high levels of insulin in the blood. [7]

EMS involves increased insulin secretion from the pancreas and lower movement of glucose into tissues. Elevated levels of insulin in the blood can induce laminitis in horses and ponies. [8][9]

Cushing’s Disease affects the pituitary gland of horses typically over the age of 15. Clinical signs of the disease include an excessively long coat that fails to shed out in the summer, depression, muscle wasting, increased water consumption and urination.

Horses with Cushing’s are at high risk of developing laminitis. This may be related to higher levels of cortisol and insulin which cause lamellar inflammation, laminitis and founder. [10]

Acute Illnesses

Health conditions including colic, diarrhea, and inflammation in the small intestine (enteritis) affect the horse’s gastrointestinal system.

These conditions may also predispose a horse to develop laminitis and subsequent founder due to the effects of toxins on the laminae.

Endotoxemia occurs when endotoxins (toxins that are produced inside cells) pass through compromised intestinal tissue and enter the bloodstream. Once in the peripheral blood supply, these toxins can alter circulation within the equine foot, increasing the risk of laminar damage and founder. [11][12]

Mares that retain their placenta after giving birth or who develop inflammation in their uterus (metritis) are at risk for endotoxemia. Conditions such as pneumonia can also cause the release of endotoxins into the bloodstream.

Overweight Body Condition

All equines can be affected by laminitis and founder regardless of their weight.

However, horses and ponies that are overweight are more at risk of pedal bone rotation and damage to their hooves because of the extra weight their feet must support.

It is important to regularly body condition score your horse and adjust their diet if they are carrying excess body fat.

Black Walnut Shavings

The use of black walnut (Juglans nigra) shavings as bedding is a known cause of laminitis After the horse is exposed to black walnut shavings via oral ingestion or skin contact, laminitis may develop within 24 to 48 hours. [13]

Oral ingestion of black walnut extract is a commonly used research technique to induce laminitis in equids. Ingestion of this substance alters blood flow to the hoof and has systemic effects on respiratory function and heart rate. [19]

Impaired Blood Supply in the Foot

Compromised blood supply to the hoof and the laminae within it can be caused by:

  • Using corticosteroid drugs over a long period of time
  • Working horses on excessively hard surfaces causing trauma to the feet
  • Standing for long periods of time in trucks

Signs and Symptoms of Founder

Laminitis and founder typically affects the front feet of horses but can occur in any of their four feet. [4]

Some of the most common clinical indications include:

  • Sudden onset of lameness
  • Resistance to walking or moving
  • Feeling a pulse and heat in the foot
  • Shifting weight back and forth between legs
  • Reluctance to bend the leg
  • Standing with the legs camped out in front of the body or with all four legs under the body
  • Laying down more frequently

Some horses develop chronic laminitis after an episode of acute laminitis. Even with chronic abnormal hoof structure, some horses may not show outwards signs of pain or lameness.

Signs to look out for that can indicate chronic laminitis and impaired hoof integrity include: [14]

  • Concavity on the dorsal side of the hoof
  • Divergent growth rings
  • Widened white line
  • Foot absesses that develop a few weeks after the initial acute laminitis episode

How is Founder Diagnosed?

Owners of horses suspected of having founder should consult with a veterinarian to obtain a precise diagnosis. Horse owners can assist their veterinarian in making a founder diagnosis by providing complete information on their horse’s medical and hoof health history.

When determining if a horse has foundered, a veterinarian will typically complete a thorough physical examination that includes assessing the behavior, weight, height, temperament, body condition score, body temperature, and vital signs of the horse.

Lameness Exam

Horses being evaluated for founder typically undergo a lameness examination that includes checking their range of motion. Hoof testing is also used to determine where the source of pain is in the foot.

Nerve Block

A nerve block may be useful for helping to diagnose founder in some cases. However, lameness due to the condition is usually evident to veterinarians in multiple other ways.

Blood Testing

Diagnostic blood testing may be used to help diagnose founder. A research study involving 22 healthy horses and 38 affected by founder determined that the latter group had reduced packed cell volume, hemoglobin, red blood cells, white blood cells, and neutrophil counts. [15]

Radiographs

In horses affected by founder, x-rays are critical for assessing the extent of the damage in the hoof including the degree of hoof rotation that has occurred. 

These images are also invaluable to farriers in helping them to choose the most appropriate therapeutic trimming and shoeing strategies to assist the recovery of the horse.

Changes including bone modelling and rotation of the coffin bone often continue to occur for several months in the hooves of horses affected by founder. X-rays should be taken on a periodic basis to determine if adjustments to the treatment plan are required.

Treatment of Founder

The sooner that treatment is started, the better the chance of recovery for an affected horse. Appropriate treatment for the condition requires addressing the underlying cause(s).

Feeding and Care Practices

In horses that have developed founder due to dietary causes, it is advised to stop feeding all grain products and remove the horse from pasture. [16]

Some horses will require treatment with a nasogastric tube to remove excess feed from their gastrointestinal tract if they have overeaten.

A foundered horse should have a soft place to stand or lie down to relieve the pressure on the weakened hoof laminae.

Depending on the severity, some horses will need stall rest whereas others may benefit from being able to move freely to promote blood circulation within the foot.

Medication

Veterinarians will typically administer non-steroidal anti-inflammatory drugs (NSAIDs) to relieve pain and inflammation in horses that have foundered.

Medication to address underlying health conditions such as Cushing’s disease may also be given.

Cold Water Therapy

To reduce inflammation in the foot, a veterinarian may suggest immersing the horse’s foot in ice water for 72 hours to maintain a consistent temperature under 40 degrees Fahrenheit.

In cases of experimentally induced laminitis, keeping the hoof in an ice bath for 48 hours prevented acute laminitis. [17]

Cold water therapy reduces blood flow to the area which lowers the amount of toxins and triggering factors that can reach the hoof.

It also inhibits inflammatory pathways in the lamellae which helps maintain a strong connection between hoof wall and coffin bone. [18]

Corrective Trimming and Shoeing

Horses with founder should be made comfortable to bear weight on the rear portion of their affected hooves.

Some horses may benefit from being shod with heart bar or egg bar shoes including therapeutic components such as pads and wedges. Barefoot trimming is used in some cases.

A priority when trimming the hooves of a foundered horse is to remove any flares on the hoof wall to reduce tension on the white line.

Surgery

Horses with founder may benefit from undergoing surgery on their deep digital flexor tendon (DDFT) to relieve tension on the structure and help prevent rotation of the coffin bone.

With prompt treatment, some horses can recover from founder. However, if the condition has caused severe damage to the hoof structure, horses may be in constant pain and unable to recover from lameness.

Key Founder Prevention Tips

Proper equine management practices aid in the prevention of founder. Consider the following strategies:

  1. Regular farrier care: Keeping the hooves in good condition helps prevent stressors that can negatively affect the structure of the laminae
  2. Veterinary wellness checks: Horses should be checked and treated for health conditions such as EMS and Cushing’s disease that may affect their hoof health
  3. Dietary monitoring: Horses should be carefully introduced to grass pastures to prevent weight gain that can cause excess weight-bearing on the hooves. Horses with metabolic concerns should not be fed grain or starchy feeds while others may be safely fed a limited amount of these food sources

If your horse has experienced laminitis in the past, it is recommended to obtain a hay analysis and work with a nutritionist to formulate an appropriate feeding plan.

For help with meeting your horse’s dietary needs, submit their diet and information online for review by our equine nutritionists.

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References

  1. Young, A. Laminitis. UC Davis. 2020.
  2. AAEP Laminitis: Prevention & Treatment. AAEP. 2021.
  3. USDA Lameness and laminitis in US Horses. USDA. 2000.
  4. Belknap, J.K. and Geor, R.J. Equine Laminitis. Wiley & Sons. 2016.
  5. Vercelli, C. et al. Effect of sugar metabolite methylglyoxal on equine lamellar explants: An ex vivo model of laminitis. PLoS One. 2021.
  6. Karikoski, N.P. et al. The prevalence of endocrinopathic laminitis among horses presented for laminitis at a first-opinion/referral equine hospital. Dom Anim Endocrin. 2011.
  7. Geor, R.J. Metabolic Predispositions to Laminitis in Horses and Ponies: Obesity, Insulin Resistance and Metabolic Syndromes. J Equine Vet Sci. 2008.
  8. de Laat, M.A. et al. Equine laminitis: induced by 48 h hyperinsulinaemia in Standardbred horses. Equine Vet J. 2010.
  9. Asplin, K.E. et al. Induction of laminitis by prolonged hyperinsulinaemia in clinically normal ponies. Vet J. 2007.
  10. Donaldson, M.T. et al. Evaluation of suspected pituitary pars intermedia dysfunction in horses with laminitis. J Am Vet Med Assoc. 2004.
  11. Tadros, E.M. et al. Effects of a “two-hit” model of organ damage on the systemic inflammatory response and development of laminitis in horses. Vet Immunol Immunopath. 2012.
  12. Visser, M.B. and Pollitt, C.C. Lamellar leukocyte infiltration and involvement of IL-6 during oligofructose-induced equine laminitis development. Vet Immunol Immunopath. 2011.
  13. OMAFRA Black Walnut and Butternut Poisoning of Horses. OMAFRA. 2016.
  14. Onishi, J.C. et al. Chronic laminitis is associated with potential bacterial pathogens in the laminae. Vet Microbiol. 2012.
  15. Ogbanya, K.C. and Ihedioha, E.J.I. Haematological and Serum Biochemical Changes in Chronic Laminitis Affected Horses. Indian J Anim Res. 2020.
  16. Watts, K. and Pollitt, C. Equine Laminitis: Managing Pasture to Reduce the Risk. Australian Government. 2010.
  17. van Eps, A.W. and Pollitt, C.C. Equine laminitis: cryotherapy reduces the severity of the acute lesion. Equine Vet J. 2010.
  18. van Eps, A.W. et al. Digital hypothermia inhibits early lamellar in?ammatory signallingin the oligofructose laminitis model. Equine Vet J. 2011.
  19. Adair III, H.S. et al. Laminar microvascular flow, measured by means of laser Doppler flowmetry, during the prodromal stages of black walnut-induced laminitis in horses. Am J Vet Res. 2000.